As a representative example of a red phosphor, for example, a sulfur-containing phosphor containing sulfur in a host material, such as (Ca, Sr)S:Eu, (Zn, Cd)(S, Se):Ag, or Ba2ZnS3:Mn, is known.
In addition, Patent Document 1 or Patent Document 2 discloses a sulfur-containing red phosphor containing calcium sulfide (CaS) as a host material, Eu as a luminescent center (activator), and Mn, Li, Cl, Ce, Gd or the like as a sensitizer (co-activator).
Further, as a green phosphor, a sulfide-based thiogallate phosphor represented by (Ca, Sr, Ba)(Al, Ga, In)2S4:Eu is known (Patent Document 3, Patent Document 4, and Patent Document 5), and as a blue phosphor, for example, a sulfur-containing phosphor, such as SrS:Ce, (Sr, Ca)Ga2S4:Ce, BaAl2S4:Eu, or Ba2SiS4:Ce, is known.
Furthermore, a core-shell type CdSe/ZnS or the like as a quantum dot phosphor in which luminescence wavelength can be adjusted by controlling the size of nanoparticles is also known (Patent Document 6).
Such a sulfur-containing phosphor containing sulfur in a host material is excited by an LED or the like, and can emit various colors of light depending on composition. Thus, the sulfur-containing phosphor has been developed as various phosphors.
However, there has been pointed out a problem in connection with this type of the sulfur-containing phosphor that hydrogen sulfide gas is generated by sulfur in the sulfur-containing phosphor, and this hydrogen sulfide gas causes, particularly in a case in which the sulfur-containing phosphor is used in a white LED element, inhibition of curing of a silicone resin that is mixed with the phosphor; corrosion of metal members inside the element, such as an Ag plating film provided so as to increase the reflectance of a lead frame (hereinafter, referred to as “Ag reflective film”), followed by a decrease in the reflection performance; or an electrical failure such as disconnection.
In this regard, hitherto, in order to enhance moisture resistance or the like, there has been proposed a method of coating this kind of phosphor with a glass material or the like (Patent Document 7, Patent Document 8, Patent Document 9, Patent Document 10, and Patent Document 11), a method of coating the surface of the phosphor particles according to a chemical gas phase reaction method (Patent Document 12), a method of attaching particles of a metal compound (Patent Document 13), or the like.
Further, Patent Document 14 discloses a ZnO compound-coated sulfur-containing phosphor having a configuration in which a ZnO compound containing Zn and O is present on the surface side of a sulfur-containing phosphor containing sulfur in a host material.